Unit 3. parameters and graphics

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1 Unit 3 parameters and graphics Special thanks to Roy McElmurry, John Kurkowski, Scott Shawcroft, Ryan Tucker, Paul Beck for their work. Except where otherwise noted, this work is licensed under:

2 Constants Python doesn't really have constants. Instead, declare a variable at the top of your code. All methods will be able to use this "constant" value. constant.py MAX_VALUE = 3 def print_top(): for i in range(max_value): for j in range(i): print(j) print() def print_bottom(): for i in range(max_value, 0, -1): for j in range(i, 0, -1): print(max_value) print() 2

3 Exercise Rewrite the Mirror lecture program in Python. Its output: #================# <><> <>...<> <>...<> <>...<> <>...<> <>...<> <>...<> <><> #================# Make the mirror resizable by using a "constant." 3

4 Exercise Solution SIZE = 4 def bar(): print("#" + 4 * SIZE * "=" + "#") def top(): for line in range(1, SIZE + 1): # split a long line by ending it with \ print(" " + (-2 * line + 2 * SIZE) * " " + \ "<>" + (4 * line - 4) * "." + "<>" + \ (-2 * line + 2 * SIZE) * " " + " ") def bottom(): for line in range(size, 0, -1): print(" " + (-2 * line + 2 * SIZE) * " " + \ "<>" + (4 * line - 4) * "." + "<>" + \ (-2 * line + 2 * SIZE) * " " + " ") # main bar() top() bottom() bar() 4

5 Parameters def name(parameter, parameter,..., parameter): statements Parameters are declared by writing their names (no types) >>> def print_many(message, n):... for i in range(n):... print(message) >>> print_many("hello", 4) hello hello hello hello 5

6 Exercise Recreate the lines/boxes of stars example from lecture: ************* ******* *********************************** ********** * * ********** ***** * * * * ***** 6

7 Exercise Solution stars.py # Draws a box of stars with the given width and height. def box(width, height): print(width * "*") for i in range(height - 2): print("*" + (width - 2) * " " + "*") print(width * "*") # main print(13 * "*") print( 7 * "*") print(35 * "*") box(10, 3) box(5, 4) 7

8 Default Parameter Values def name(parameter=value,..., parameter=value): statements Can make parameter(s) optional by specifying a default value >>> def print_many(message, n=1):... for i in range(n):... print(message) >>> print_many("shrubbery") shrubbery >>> print_many("shrubbery", 3) shrubbery shrubbery shrubbery Exercise: Modify stars.py to add an optional parameter for the character to use for the outline of the box (default "*"). 8

9 Parameter Keywords name(parameter=value,..., parameter=value) Can specify name of each parameter as you call a function This allows you to pass the parameters in any order >>> def print_many(message, n):... for i in range(n):... print(message) >>> print_many(str="shrubbery", n=4) shrubbery shrubbery shrubbery shrubbery >>> print_many(n=3, str="ni!") Ni! Ni! Ni! 9

10 DrawingPanel Instructor-provided drawingpanel.py file must be in the same folder as your Python program At the top of your program, write: from drawingpanel import * Panel's canvas field behaves like Graphics g in Java 10

11 DrawingPanel Example draw1.py from drawingpanel import * panel = DrawingPanel(400, 300) panel.set_background("yellow") panel.canvas.create_rectangle(100, 50, 200, 300) 11

12 Drawing Methods Java drawline drawrect, fillrect drawoval, filloval drawstring Python panel.canvas.create_line(x1, y1, x2, y2) panel.canvas.create_rect(x1, y1, x2, y2) panel.canvas.create_oval(x1, y1, x2, y2) panel.canvas.create_text(x, y, text="text") setcolor setbackground (see next slide) panel.set_background(color) Notice, methods take x2/y2 parameters, not width/height 12

Colors and Fill Python doesn't have fillrect, filloval, or setcolor. Instead, pass outline and fill colors when drawing a shape. List of all color names: http://wiki.tcl.

13 Colors and Fill Python doesn't have fillrect, filloval, or setcolor. Instead, pass outline and fill colors when drawing a shape. List of all color names: See class web site for visual index of colors! drawcolors.py from drawingpanel import * panel = DrawingPanel(400, 300) panel.canvas.create_rectangle(100, 50, 200, 200, outline="red", fill="yellow") panel.canvas.create_oval(20, 10, 180, 70, fill="blue") 13

14 Polygons Draw arbitrary polygons with create_polygon Draw line groups by passing more params to create_line drawpoly.py from drawingpanel import * panel = DrawingPanel(200, 200) panel.canvas.create_polygon(100, 50, 150, 0, 150, 100, fill="green") panel.canvas.create_line(10, 120, 20, 160, 30, 120, 40, 175) 14

Exercise Write a Python version of the Car program. Convert this Java code to Python: DrawingPanel panel = new DrawingPanel(200, 200); panel.setbackground(color.light_gray); Graphics g = panel.

15 Exercise Write a Python version of the Car program. Convert this Java code to Python: DrawingPanel panel = new DrawingPanel(200, 200); panel.setbackground(color.light_gray); Graphics g = panel.getgraphics(); g.setcolor(color.black); // body g.fillrect(10, 30, 100, 50); g.setcolor(color.red); // wheels g.filloval(20, 70, 20, 20); g.filloval(80, 70, 20, 20); g.setcolor(color.cyan); // windshield g.fillrect(80, 40, 30, 20); 15

16 Exercise Modify your car program to use parameters so that cars can be drawn in many different locations. 16

17 Exercise Write a variation of the Car program where the car body is octagonal and there is a stop sign Stop sign at (150, 10), size 40 post at (165, 50), size 10x30, brown fill Write an octagon function to draw the car body / stop sign. Points of car body, located at (10, 10): 1. (10, 20), 2. (20, 10), 3. (100, 10), 4. (110, 20), 5. (110, 50), 6. (100, 60), 7. (20, 60), 8. (10, 50) Points of stop sign, located at (150, 10): 1. (150, 20), 2. (160, 10), 3. (180, 10), 4. (190, 20), 5. (190, 40), 6. (180, 50), 7. (160, 50), 8. (150, 40) (An octagon has 10x10 triangular cuts in each corner.) 17

18 Animation Pause the panel by calling sleep animation.py from drawingpanel import * panel = DrawingPanel(350, 300) for i in range(20): # clear any previous image panel.canvas.create_rectangle(0, 0, 400, 400, outline="white", fill="white") panel.canvas.create_polygon(20 * i, 50, 20 * i, 100, 20 * i + 50, 75) panel.sleep(100) 18

19 Exercise Animate the car to make it drive across the panel using the sleep function. 19

Week 3. parameters, return, math, graphics

Week 3. parameters, return, math, graphics Week 3 parameters, return, math, graphics Special thanks to Scott Shawcroft, Ryan Tucker, and Paul Beck for their work on these slides. Except where otherwise noted, this work is licensed under: http://creativecommons.org/licenses/by-nc-sa/3.0